WO2018094850A1

WO2018094850A1 - Test head for testing fingerprint sensor

Info

Publication number: WO2018094850A1
Application number: PCT/CN2016/113928
Authority: WO
Inventors: 林娇; 古蒋林
Original assignee: 华为技术有限公司
Priority date: 2016-11-26
Filing date: 2016-12-30
Publication date: 2018-05-31
Also published as: WO2018094850A9; CN108604295A

Abstract

Disclosed is a test head (100) for testing a fingerprint sensor. The test head (100) comprises: a functional layer (110), the material of the functional layer (110) being related to the type of the fingerprint sensor, and the functional layer (110) comprising a first surface (111) and a second surface (112) opposite to each other, with the first surface (111) comprising a pattern; and a support layer (120), the material of the support layer (120) being a kind of insulating material which simulates the softness of a human hand, and the support layer (120) being adhesively bonded to the functional layer (110) via the second surface (112). With respect to the test head of the prior art, the test head (100) has a greater flexibility, and can simulate the effect of a human hand directly pressing the fingerprint sensor to a greater degree.

Description

Test head for testing fingerprint sensors

Technical field

The present application relates to the field of fingerprint sensor testing technology and, more particularly, to a test head for testing a fingerprint sensor.

Background technique

In recent years, fingerprint unlocking is almost standard on smartphones and tablet devices, which makes the unlocking function more convenient and ensures the security of smart devices. The quality of the fingerprint sensor output image directly affects the unlocking performance, so the fingerprint sensor image quality needs to be tested and controlled in the production line. The existing test method in the industry is to press a standard test head (for the capacitive fingerprint sensor to be grounded) to the sensor surface with a certain pressure. The sensor triggers the image acquisition function, outputs the image, and scores the image quality of the sensor through image analysis. Control of sensor performance.

Since the conductive silicone material is soft and does not damage the sensor surface, and the conductive property is easier to ground, it is the most widely used material for making standardized test heads in the industry.

The design of the test head in the prior art has a single design structure, and cannot flexibly imitate the effect of directly pressing the fingerprint sensor by the human hand, thereby failing to meet the requirements of a complicated test environment.

Summary of the invention

The application provides a test head for testing a fingerprint sensor, which has greater flexibility and can simulate the effect of directly pressing the fingerprint sensor by a human hand.

In a first aspect, a test head for testing a fingerprint sensor is provided, the test head comprising: a functional layer, a material of the functional layer being related to a type of the fingerprint sensor, the functional layer including an opposite first surface And the second surface, the first surface includes a pattern; the support layer is made of an insulating material simulating human hand softness, and the supporting layer and the functional layer are bonded through the second surface .

The type of the fingerprint sensor is for the detected physical quantity of the fingerprint sensor. Specifically, the type of the fingerprint sensor includes a capacitive fingerprint sensor, an ultrasonic fingerprint sensor, an optical fingerprint sensor, and the like.

The test head provided by the solution for testing the fingerprint sensor adopts a multi-layer structure (including a functional layer and a support layer), and enables different layers to simulate different dimensions of biological characteristics (the functional layer includes a pattern of a simulated human hand pattern, and the support layer is adopted. The material for simulating the softness of the human hand has greater flexibility than the prior art test head, and can greatly simulate the effect of directly pressing the fingerprint sensor by a human hand.

In a possible implementation manner, the pattern on the first surface comprises an uneven pattern, for example, the pattern on the first surface is a pattern simulating a human hand fingerprint to achieve an image effect similar to a human hand touch.

In a possible implementation manner, when the test head tests the fingerprint sensor, the first surface is used to press on a fingerprint sensing area of the fingerprint sensor.

In conjunction with the first aspect, in a possible implementation manner, the fingerprint sensor is a capacitive fingerprint sensor, and the functional layer is made of a conductive material with stable conductivity, and the functional layer includes leads for grounding.

In the current technology, the test head for testing the capacitive fingerprint sensor is realized by using conductive silica gel. Since the conductive silica material is electrically conductive by doping conductive particles, the conductivity of the conductive silica gel is sensitive to pressure, resulting in poor test repeatability of the test head. It affects the accuracy of the determination of the performance of the fingerprint sensor and the efficiency of the production line test.

The test head provided by the solution for testing the capacitive fingerprint sensor comprises a functional layer with a material with stable conductivity and a support layer with a material for simulating the softness of the human hand, and the functional layer can be grounded, and the grounding resistance is relatively stable. Compared with the traditional capacitive test head, it has better electrical conductivity stability, so that it has better test repeatability and improves test efficiency.

In conjunction with the first aspect, in a possible implementation, the functional layer includes at least one via, the at least one via electrically connecting the first surface to the second surface, the lead from the A portion of the two surfaces electrically connected to the at least one via is taken out.

In the present solution, the grounding of the functional layer 110 is achieved by the via between the first surface 111 and the second surface 112, and the second surface leads to the ground lead, so that the test head for testing the capacitive fingerprint sensor is grounded. The impedance is small and stable.

With reference to the first aspect, in a possible implementation manner, the pattern of the first surface is a diagonal stripe, the edge of the first surface includes a conductive layer, and each of the conductive layer and the diagonal stripe Strips are electrically connected.

In a possible implementation manner, it is also possible to make a copper leakage on the surface of the pattern of the first surface. Further, a gold layer is further plated on the surface of the pattern, for example, the thickness of the gold layer is 4-6 um to prevent oxidation of the copper leakage.

In combination with the first aspect, in a possible implementation manner, the functional layer is made of any one of the following metals: copper, gold or silver.

In conjunction with the first aspect, in a possible implementation manner, the fingerprint sensor is an ultrasonic fingerprint sensor, and the functional layer is made of a material whose impedance is close to the impedance of the human hand.

In a possible implementation manner, the fingerprint sensor is an ultrasonic fingerprint sensor, and the functional layer is made of polyvinylidene chloride PVD.

In combination with the first aspect, in a possible implementation manner, the fingerprint sensor is an optical fingerprint sensor, and the functional layer is made of a material whose refractive index is close to the refractive index of the human hand.

In a possible implementation manner, the fingerprint sensor is an optical fingerprint sensor, and the functional layer is made of pig skin or latex.

In combination with the first aspect, in a possible implementation manner, the pattern of the first surface is any one of the following patterns: diagonal stripes, back-shaped or small holes.

In a possible implementation manner, a more complicated pattern including a sweat hole, an end point, a bend, and the like may also be designed on the first surface 111.

In combination with the first aspect, in a possible implementation manner, the material of the support layer is any one of the following materials: non-conductive silica gel, polydimethylsiloxane PDMS, and resin-based materials.

In a possible implementation, the support layer can also be shaped to simulate the contour of a human hand.

Based on the above analysis, the test head for testing a fingerprint sensor provided by the present application adopts a multi-layer structure (including a functional layer and a support layer), and causes different layers to simulate different dimensions of biological characteristics (the functional layer includes a pattern of a simulated human hand pattern) The support layer adopts a material that simulates the softness of the human hand. Compared with the test head in the prior art, the utility model has greater flexibility, and can simulate the effect of directly pressing the fingerprint sensor by a human hand.

DRAWINGS

FIG. 1A and FIG. 1B are schematic diagrams of a test head for testing a fingerprint sensor according to an embodiment of the present invention.

2A, FIG. 2B and FIG. 2C are schematic diagrams showing patterns on a functional layer of a test head for testing a fingerprint sensor according to an embodiment of the present invention.

FIG. 3 is a schematic diagram of a test head for testing a capacitive fingerprint sensor according to an embodiment of the present invention.

4 is a schematic diagram of an image acquired by using the test head shown in FIG. 3 to test a capacitive fingerprint sensor.

detailed description

The technical solutions in the embodiments of the present invention will be described below with reference to the accompanying drawings.

The fingerprint sensor (also known as Fingerprint Sensor) is the key device for automatic fingerprint acquisition. The fingerprint sensor is divided into an optical fingerprint sensor, a capacitive fingerprint sensor, an ultrasonic sensor, etc. according to the sensing principle, that is, the principle and technology of fingerprint imaging.

Fingerprint sensors are widely used in the field of fingerprint unlocking or fingerprint anti-counterfeiting detection of smart devices. The quality of the fingerprint sensor output image directly affects the application performance of the fingerprint sensor. Therefore, the fingerprint sensor production line needs to test and control the image quality of the fingerprint sensor. Currently, the industry test method is to press a standard test head to the surface of the fingerprint sensing area of the fingerprint sensor with a certain pressure. The fingerprint sensor triggers the image acquisition function, outputs an image, and scores the image quality of the fingerprint sensor through image analysis, thereby achieving The image quality of the fingerprint sensor is controlled.

Since the material of the conductive silica gel does not damage the sensor surface, and the conductive property of the conductive silica gel is easier to ground, the conductive silica gel is the most widely used material for making standardized test heads in the industry.

In addition, the conductive silica gel uniformly distributes conductive particles such as nickel-coated copper powder and silver powder in the silica gel, and contacts the conductive particles by pressure to achieve electrical conductivity. However, since the conductive silica gel is electrically conductive by doping the conductive particles, its conductivity is sensitive to pressure, resulting in poor test repeatability of the test head, affecting the accuracy of the determination of the performance of the fingerprint sensor and the efficiency of the production line test.

In view of the above technical problem, the embodiment of the present invention provides a test head for testing a fingerprint sensor, which has greater flexibility than the test head in the prior art, and can simulate a human hand directly pressing the fingerprint sensor to a large extent. The effect, but also overcome the shortcomings of test repeatability.

1A is a schematic cross-sectional view of a test head 100 for testing a fingerprint sensor according to an embodiment of the present invention. The test head 100 includes a functional layer 110 and a support layer 120. The functional layer 110 includes opposing first surfaces 111 and second. Surface 112. In order to facilitate the second surface 112, in Figure 1 There is a gap between the functional layer 110 and the support layer 120. It should be understood that, in practical applications, the functional layer 110 and the support layer 120 are bonded together through the second surface 112, and specifically, may be bonded by double-sided adhesive. It can also be bonded by other materials having a bonding function, which is not limited in the embodiment of the present invention. It should be understood that the bonding substance between the functional layer 110 and the support layer 120 may also be referred to as an intermediate layer of the test head 100.

FIG. 1B is a top view of a test head 100 for testing a fingerprint sensor according to an embodiment of the present invention. Specifically, the view direction of the top view refers to a direction from the functional layer 110 toward the support layer 120. As shown in FIG. 1B, the plane of the functional layer 110 (the plane in which the first surface 111 is located) is completely within the plane of the support layer 120 in the direction of the top view. Specifically, the area of the plane of the functional layer 110 (the plane in which the first surface 111 is located) is smaller than or equal to the area of the plane of the support layer 120.

The material of the functional layer 110 is related to the type of the fingerprint sensor.

The type of the fingerprint sensor is divided based on the detected physical quantity of the fingerprint sensor. For example, based on the difference in the detected physical quantity, the fingerprint sensor includes the following types: a capacitive fingerprint sensor, an ultrasonic fingerprint sensor, and an optical fingerprint sensor.

Specifically, when the fingerprint sensor is a capacitive fingerprint sensor, the functional layer 110 needs to be made of a conductive material and is a material with stable conductivity, such as a conductive metal material such as copper, gold or silver. When the fingerprint sensor is an ultrasonic fingerprint sensor, the functional layer 110 needs to adopt a material whose impedance is close to the impedance of the human hand, such as polyvinylidene chloride PVD or other polymers. When the fingerprint sensor is an optical fingerprint sensor, the functional layer 110 needs to adopt a material whose refractive index is close to the refractive index of the human hand, such as pig skin, latex, and the like.

The first surface 111 includes a pattern.

Optionally, the first surface 111 includes an uneven pattern, for example, the first surface 111 includes a pattern simulating a human hand fingerprint (ridge and valley) to achieve an image effect similar to a human hand touch.

It should be understood that the fingerprint is a raised line on the human skin, the raised portion may be referred to as a ridge (or ridge), and the concave portion may be referred to as a valley (or ridge). Fingerprints have three basic shapes: spiral, circular, and arcuate. The regional feature patterns of the overall characteristics of the fingerprint include: core points, triangle points, and pattern lines. The local features of the fingerprint (nodes on the fingerprint) include: endpoints, bifurcation points, isolated points and center points.

Specifically, the pattern on the first surface 111 may be a retro-shaped shape as shown in FIG. 2A; or the pattern on the first surface 111 may be a diagonal stripe as shown in FIG. 2B.

It should also be understood that the pattern included on the first surface 111 may not be uneven, and the pattern included on the first surface 111 may be such that the fingerprint sensor under test can acquire an image. can.

Specifically, the pattern on the first surface 111 is an aperture as shown in FIG. 2C.

It should be noted that, besides the patterns shown in FIG. 2A, FIG. 2B and FIG. 2C, more complicated patterns including sweat holes, end points, bends, and the like may be designed on the first surface 111 according to test requirements. The comparison of the examples is not limited.

It should be understood that when the test head 100 is put into application, the first surface 111 is pressed on the surface of the fingerprint sensing area of the fingerprint sensor.

The material of the support layer 120 is not conductive, and the material of the support layer is a material simulating the softness of the human hand.

Specifically, materials that can be selected for the support layer 120 include, but are not limited to, non-conductive silicone, polydimethylsiloxane PDMS, and resin-based materials.

It should be understood that the support layer 120 adopts a soft material simulating the softness of the human hand. When the test head 100 is pressed onto the fingerprint sensor, the test head 100 and the surface of the fingerprint sensing area of the fingerprint sensor are easily and seamlessly fitted. The effect of touching the fingerprint sensor by a human hand is largely simulated.

Alternatively, the support layer 120 can be fabricated into regular squares by injection molding techniques.

Alternatively, the support layer 120 can also be shaped to mimic the contours of a human hand.

Specifically, for example, in conjunction with the manufacturing process of the finger mold, the support layer 120 is made into a model simulating a human finger contour.

A test head for testing a fingerprint sensor provided by an embodiment of the present invention adopts a multi-layer structure (including a functional layer and a support layer), and causes different layers to simulate different dimensions of biological characteristics (the functional layer includes a pattern of a simulated human hand pattern, and supports The layer adopts a material that simulates the softness of the human hand), and has greater flexibility than the test head in the prior art, and can greatly simulate the effect of directly pressing the fingerprint sensor by the human hand.

It should be understood that the functional layer 110 in the test head 100 of the embodiment of the present invention may be deformed correspondingly according to the deformation of the support layer 120. In other words, the thickness of the functional layer 110 is small, enabling it to deform as the support layer 120 is deformed.

Optionally, in some embodiments, the fingerprint sensor is a capacitive fingerprint sensor, and the functional layer 110 is made of a conductive material with stable conductivity, and the functional layer 110 includes leads for grounding.

It should be understood that the working principle of the capacitive fingerprint sensor is that the ridges and valleys of the finger touch the surface of the capacitive sensor to form an image with a difference in capacitance, and the gray image is output after a certain processing. Specifically, according to the difference of the detection capacitance value, it is divided into two working modes: self-capacity and mutual capacitance. Each pixel array of the self-capacitance fingerprint sensor is a capacitor plate, and the ridges and valleys of the fingerprint form different capacitance values between the valley and the pixel array plate, thereby generating an image. The mutual-capacitance fingerprint sensor consists of Rx and Tx layers. The ridges and valleys of the fingerprint produce different capacitance values at the intersection of Rx and Tx to generate an image. Therefore, the test head used to test the capacitive fingerprint sensor needs to have conductive and grounding functions.

Specifically, in the embodiment of the present invention, the material of the functional layer 110 may be any one of the following metals: copper, gold or silver.

Specifically, in the embodiment of the present invention, the grounding line of the functional layer 110 can be taken out from any position of the functional layer 110.

Preferably, in the embodiment of the present invention, the functional layer 110 includes at least one via, the at least one via electrically connecting the first surface 111 and the second surface 112, and the lead for grounding is from the second surface 112. The upper portion is electrically connected to the at least one via hole.

Specifically, as shown in FIG. 3, FIG. 3 is a schematic diagram of a test head for testing a capacitive fingerprint sensor. The pattern on the first surface 111 of the test head is a diagonal strip as shown in Figure 2B. The edge of the first surface 111 includes a turn-on conductive layer that is electrically connected to each of the stripe patterns. A via 140 is formed on the four opposite corners of the first surface 111. The via 140 is electrically connected to the conductive layer, and the via 140 is used to electrically conduct the first surface 111 and the second surface 112 (not shown in FIG. 3 show). The lead 130 for grounding is taken from a position on the second surface 112 that is electrically connected to the via 140. Specifically, two leads 130 may be provided. Preferably, as shown in FIG. 3, the two leads 130 may be from two Lead out at a symmetrical position.

In the embodiment of the present invention, the grounding of the functional layer 110 is achieved by the via between the first surface 111 and the second surface 112 and the grounding lead of the second surface, so that the grounding impedance of the test head is small and stable. .

It should be understood that, in FIG. 3, the two lead wires 130 for grounding are taken as an example. However, in actual applications, the number of the grounding wires 130 may be determined according to specific conditions, which is not limited in the embodiment of the present invention.

Specifically, in the embodiment of the present invention, the functional layer 110 can be fabricated by using the current mature soft board process.

Alternatively, in some embodiments, after the pattern imitating the texture of the human hand is formed on the first surface 111, a copper leakage process may also be performed on the surface of the pattern. In order to prevent leakage of copper oxide, a gold layer may be further plated on the surface of the pattern, for example, the thickness of the gold layer is 4-6 um.

Specifically, when the capacitive fingerprint sensor is tested using the test head shown in FIG. 3, the image acquired by the capacitive fingerprint sensor is as shown in FIG. 4.

It should be understood that the test head used to test the capacitive fingerprint sensor may be referred to as a capacitive test head.

The capacitive test head in the prior art is realized by using conductive silica gel. Since the conductive silica material is electrically conductive by doping conductive particles, the conductivity of the conductive silica gel is sensitive to pressure, resulting in poor test repeatability of the test head, affecting the fingerprint sensor. Performance determination accuracy and production line test efficiency.

The capacitive test head provided by the embodiment of the invention includes a functional layer with a material with stable conductivity and a support layer with a material for simulating the softness of the human hand, and the functional layer can be grounded, and the grounding resistance is relatively stable, compared with the conventional The capacitive test head has better electrical conductivity stability, so that it has better test repeatability and improves test efficiency.

The test head for testing the capacitive fingerprint sensor provided by the embodiment of the present invention is described above with reference to FIG. 3 and FIG. 4 , but the embodiment of the present invention is not limited thereto, and the adaptive trimming function layer 110 is provided by the embodiment of the present invention. The test head 100 (shown in Figures 1A and 1B) can be applied to any type of fingerprint sensor.

Optionally, in some embodiments, the fingerprint sensor is an ultrasonic fingerprint sensor, and the functional layer is made of a material whose impedance is close to the impedance of the human hand.

For example, under dry conditions, the body impedance is about 1000 to 3000 Ω. When the fingerprint sensor is an ultrasonic fingerprint sensor, the functional layer may be made of a material having an impedance of 1000 to 3000 Ω. It should be understood that the impedance of the human body may be different under different environmental conditions, and the above examples are merely examples and are not limiting. In practical applications, an impedance tester can be used to measure the impedance of a human hand, and then a material close to the measured impedance can be selected to make a functional layer. Specifically, the functional layer is made of polyvinylidene chloride PVD.

It should be understood that the ultrasonic fingerprint sensor uses the piezoelectric material to generate an ultrasonic signal, and passes through the laminated structure of the fingerprint to reach the interface between the finger and the surface layer, and the fingerprint image can be detected by utilizing the characteristics of the reflectivity of the ultrasonic wave and the impedance difference between the two sides of the interface. Specifically, the greater the difference in impedance between the two sides of the interface, the greater the reflectivity of the ultrasonic waves. The valley of the fingerprint is equivalent to the air layer, and the ultrasonic wave reaches the surface medium and the valley is almost completely reflected. In contrast, the ultrasonic wave reaches the surface medium and the ridge is mostly transmitted to form the difference of the image.

Optionally, in some embodiments, the fingerprint sensor is an optical fingerprint sensor, and the functional layer is made of a material whose refractive index is close to the refractive index of the human hand.

In practical applications, the refractive index of the finger can be measured by an optical instrument, and then the functional layer 110 can be made by selecting a material that is close to the refractive index of the human hand. Specifically, for example, the functional layer can be produced by selecting materials such as pig skin, latex, and the like.

It should be understood that the principle of the optical fingerprint sensor is to image the difference in the reflectance of the light using the ridges of the fingerprint. Specific implementation devices include an LED light source, an imaging optical path, and a photodiode detector (PD). The PD may be a device based on a Complementary Metal Oxide Semiconductor (CMOS) device or a glass substrate.

It should be noted that the functional layer of the test head for testing the fingerprint sensor provided by the embodiment of the present invention may be replaced. For example, when the capacitive fingerprint sensor needs to be tested, the functional layer of the test head is replaced with the corresponding function of the capacitive test head. Layer; when testing the ultrasonic fingerprint sensor, replace the functional layer of the test head with the functional layer corresponding to the ultrasonic test head; when testing the optical fingerprint sensor, replace the functional layer of the test head with the functional layer corresponding to the optical test head.

It should be understood that the above is mainly described by using a test head for testing a capacitive fingerprint sensor, an ultrasonic fingerprint sensor, and an optical fingerprint sensor, but the embodiment of the present invention is not limited thereto. The test head for testing the fingerprint sensor provided by the embodiment of the present invention can be applied to other various fingerprint sensors, as long as the material and design of the functional layer are reasonably determined according to the physical characteristics of the physical quantity detected by the fingerprint sensor.

The embodiment of the invention can be applied to a production line of a fingerprint sensor production line or a fingerprint sensor in a smart device assembly such as a mobile phone/tablet, which is used for controlling the quality of the fingerprint image, intercepting a product with poor image quality, and ensuring product performance.

In the fingerprint detection application, a mechanical arm that can be moved up and down and the pressure is controllable is required, and the test head for testing the fingerprint sensor provided by the embodiment of the present invention is installed at the end of the mechanical arm. The fingerprint sensor is mounted on a dedicated stage. By controlling the robot arm, the test head can be pressed onto the surface of the fingerprint sensing area of the fingerprint sensor, and the fingerprint sensor collects the fingerprint image. After the fingerprint image is collected, the test head is raised by controlling the robot arm to complete the test of the fingerprint sensor. The specific process is: Step1, placing the fingerprint sensor on the stage. Step 2, pressing the robot arm such that the first surface of the test head is pressed against the surface of the fingerprint sensing area of the fingerprint sensor. Step3, the fingerprint sensor performs image acquisition. Step 4, the collected image is sent to an algorithm module, and the algorithm module is used to evaluate the collected image. The algorithm mentioned in Step 4, the algorithm used by different manufacturers of fingerprint sensors is different, and will not be described in detail here. Step5, lift the arm and complete the test.

It should also be understood that the various numerical numbers referred to herein are merely for convenience of description and are not It is intended to limit the scope of the embodiments of the invention.

It should be understood that, in the embodiment of the present invention, the size of the sequence numbers of the foregoing processes does not mean the order of execution sequence, and the execution order of each process should be determined by its function and internal logic, and should not be implemented in the embodiment of the present invention. Form any limit.

The foregoing is only a specific embodiment of the present application, but the scope of protection of the present application is not limited thereto, and any person skilled in the art can easily think of changes or substitutions within the technical scope disclosed in the present application. It should be covered by the scope of protection of this application. Therefore, the scope of protection of the present application should be determined by the scope of the claims.

Claims

A test head for testing a fingerprint sensor, comprising:

a functional layer, the material of the functional layer is related to the type of the fingerprint sensor, the functional layer includes an opposite first surface and a second surface, and the first surface includes a pattern;

The support layer is made of an insulating material that simulates the softness of a human hand, and the support layer and the functional layer are bonded by the second surface.
The test head according to claim 1, wherein the fingerprint sensor is a capacitive fingerprint sensor, and the functional layer is made of a conductive material having a stable conductivity, and the functional layer includes a lead for grounding.
The test head according to claim 2, wherein said functional layer comprises at least one via, said at least one via electrically connecting said first surface to said second surface, said lead being from said A portion of the two surfaces electrically connected to the at least one via is taken out.
The test head according to claim 3, wherein the first surface comprises a pattern of diagonal stripes, the edge of the first surface comprises a conductive layer, and the conductive layer and the diagonal stripe Each strip is electrically connected.
The test head according to any one of claims 2 to 4, wherein the functional layer is made of any one of the following metals: copper, gold or silver.
The test head according to claim 1, wherein the fingerprint sensor is an ultrasonic fingerprint sensor, and the functional layer is made of a material whose impedance is close to the impedance of the human hand.
The test head according to claim 6, wherein the functional layer is made of polyvinylidene chloride PVD.
The test head according to claim 1, wherein the fingerprint sensor is an optical fingerprint sensor, and the functional layer is made of a material whose refractive index is close to the refractive index of the human hand.
The test head according to claim 8, wherein the functional layer is made of pig skin or latex.
The test head according to any one of claims 1 to 3, 5 to 8, wherein the first surface comprises a pattern of any one of the following patterns: diagonal stripes, back-shaped or small holes.
The test head according to any one of claims 1 to 10, wherein the support layer is made of any one of the following materials: non-conductive silicone, polydimethylsiloxane PDMS, and resin. Class materials.